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Machine Mart's Buyers Guide To Drills & Drilling
Electric drills fall into two main categories – Portable (hand held) or Stationary.
HAND HELD POWER DRILLS
The electric drill is probably the most essential tool for any tool kit. It is usually the first, if not the only power tool in the most basic DIY’ers kit as it is such a flexible tool. Apart from the obvious – drilling holes in wood, plastic, masonry and metal, with the correct attachments, they may also be used for grinding, cutting, sanding, screwdriving or mixing paint etc. The range of drills available for the professional user is massive and the possible uses are even more extensive.
Types of hand held electric drill Basic - Single speed without hammer. These are suitable for the novice DIY user, who just needs to drill holes in wood metal or plastic. Hammer Drill – These apply a hammer action in the direction of drilling which enables you to drill in concrete or masonry Cordless – These give you more freedom as you don’t need trailing power leads to supply them. They vary from 3.6 volts for DIY cordless screwdrivers to 36 volts for the professional tradesmen’s models. Demolition Hammer/Breakers – Heavy duty machines for – you guessed it! Demolition and breaking masonry and concrete. Impact Wrench – These specialist tools apply a powerful hammer action in a rotary direction to loosen stubborn nuts and bolts.
Key features of portable drills
Speed – The larger the diameter of the drill used, the slower the speed should be. Variable speed – Allows slow starts and drilling in different materials. Chuck Size – This determines the maximum drill bit size. Drilling capacity – The maximum drill size for certain materials Reverse – Useful for screwdriving. Torque setting – Allows screws to be tightened to a pre-determined setting. Keyless chuck – Allows you to change bits without a chuck key Kit box- A handy box for carrying/storing the drill and its accessories. Watts – The power of the machine, the higher this figure, the larger jobs it can handle. Hammer action – Should be used when drilling masonry or concrete. SDS (Slotted Drive System) – This is an advanced hammer system with a positive bayonet chuck mechanism, which is capable of delivering far more torque. These machines have drill and drill/hammer action. Some also have rotation stop for chiseling. SDS+ - This is a larger version of SDS, which is capable of handling even more power, making it suitable for the heaviest tasks. Impact energy – Shown in Joules indicates the power of each “hammer” blow Blows per minute – Indicates how fast the hammer action is.
Health and Safety
As with all power tools care should be taken when using an electric drill. Depending on what you are drilling, personal protective equipment should include goggles, gloves and ear defenders. Also your clothing should not be able to become entangled in the drill and long hair should be tied back.
Consideration should also be given to what you are drilling, if it’s small, it should be clamped, when drilling walls, you should check that there are no pipes or wires where you are drilling. There are a range of pipe and wire detectors available from Machine Mart.
All drills these days are double insulated, which means that no earth is required, but safety is still maintained. However, if drilling near water or out-doors it is recommended to use a Residual Current Device (RCD).
Types Of Drill Bit
There are several types of drill bit, some designed with specific tasks in mind, others suitable for general drilling. The most common are twist drill bits, which have helical groves in them, to allow for the removal of swarf (waste material).
Types of twist drill
High Speed Steel (HSS) - Suitable for general drilling in wood, metal and plastics. Titanium Coated - This coating (usually gold coloured) can last up-to six times longer than standard drill bits. Cobalt steel - Provides higher heat and abrasion resistance making these bits suitable for drilling hardened steel, stainless steel and titanium. Blacksmiths drills - Have a smaller shank than the drill diameter, allowing for example a 15mm drill bit to be used in a drill with a 13mm chuck.
Spur pointed or dowel bits - Are specifically designed to accurately drill holes in wood. As they have a lesser tendency to wander from centre.
Masonry bits - These drill bits have an extra hard Tungsten Carbide tip to allow them to drill masonry and concrete. Masonry bits can have Standard, SDS or SDS+ shanks.
Wood boring Augers - Used for making larger holes in wood, at slower speeds, they may also be used in hand powered braces.
Other types of drill bits
Flat wood bits - Used for quickly boring large holes in wood, they are less accurate than the augers.
Forstner bits - Again used for making larger, flat bottomed holes in wood, for cabinet door hinges etc, they may also be used in more than one plane.
Hole cutters - These bits, with a bi-metallic saw blade are suitable for cutting holes in a variety of materials, metal, plastic, thin wood, plaster etc.
Glass and tile bits - Specialist bits, with a Tungsten carbide tip, designed to be used at slow speeds, to drill tiles and glass.
| Decimal inch | metric mm | decimal inch | metric mm | | 0.013 | 0.3302 | 0.144 | 3.6576 | | 0.014 | 0.3556 | 0.147 | 3.7338 | | 0.015 | 0.3810 | 0.1495 | 3.7973 | | 0.016 | 0.4064 | 0.152 | 3.8608 | | 0.018 | 0.4572 | 0.154 | 3.9116 | | 0.020 | 0.5080 | 0.157 | 3.9878 | | 0.022 | 0.5588 | 0.159 | 4.0386 | | 0.023 | 0.5842 | 0.161 | 4.0894 | | 0.024 | 0.6096 | 0.166 | 4.2164 | | 0.026 | 0.6604 | 0.1695 | 4.3053 | | 0.027 | 0.6858 | 0.173 | 4.3942 | | 0.029 | 0.7366 | 0.177 | 4.4958 | | 0.030 | 0.7620 | 0.180 | 4.5720 | | 0.031 | 0.7874 | 0.182 | 4.6228 | | 0.032 | 0.8128 | 0.185 | 4.6990 | | 0.033 | 0.8382 | 0.189 | 4.8006 | | 0.035 | 0.8890 | 0.191 | 4.8514 | | 0.036 | 0.9144 | 0.1935 | 4.9149 | | 0.037 | 0.9398 | 0.196 | 4.9784 | | 0.038 | 0.9652 | 0.199 | 5.0546 | | 0.039 | 0.9906 | 0.201 | 5.1054 | | 0.041 | 1.0414 | 0.204 | 5.1816 | | 0.042 | 1.0668 | 0.2055 | 5.2197 | | 0.043 | 1.0922 | 0.209 | 5.3086 | | 0.0465 | 1.1811 | 0.213 | 5.4102 | | 0.052 | 1.3208 | 0.221 | 5.6134 | | 0.055 | 1.3970 | 0.228 | 5.7912 | | 0.0595 | 1.5113 | 0.234 | 5.9436 | | 0.0635 | 1.6129 | 0.238 | 6.0452 | | 0.067 | 1.7018 | 0.242 | 6.1468 | | 0.070 | 1.7780 | 0.246 | 6.2484 | | 0.073 | 1.8542 | 0.250 | 6.3500 | | 0.076 | 1.9304 | 0.257 | 6.5278 | | 0.0785 | 1.9939 | 0.261 | 6.6294 | | 0.081 | 2.0574 | 0.266 | 6.7564 | | 0.082 | 2.0828 | 0.272 | 6.9088 | | 0.086 | 2.1844 | 0.277 | 7.0358 | | 0.089 | 2.2606 | 0.281 | 7.1374 | | 0.0935 | 2.3749 | 0.290 | 7.3660 | | 0.096 | 2.4384 | 0.295 | 7.4930 | | 0.098 | 2.4892 | 0.302 | 7.6708 | | 0.0995 | 2.5273 | 0.316 | 8.0264 | | 0.1015 | 2.5781 | 0.323 | 8.2042 | | 0.104 | 2.6416 | 0.332 | 8.4328 | | 0.1065 | 2.7051 | 0.339 | 8.6106 | | 0.110 | 2.7940 | 0.348 | 8.8392 | | 0.111 | 2.8194 | 0.358 | 9.0932 | | 0.113 | 2.8702 | 0.368 | 9.3472 | | 0.116 | 2.9464 | 0.377 | 9.5758 | | 0.120 | 3.0480 | 0.386 | 9.8044 | | 0.1285 | 3.2639 | 0.397 | 10.0838 | | 0.136 | 3.4544 | 0.404 | 10.2616 | | 0.1405 | 3.5687 | 0.413 | 10.4902 |
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